Knife sharpener



FIG. 1 is a top plan view of a knife sharpener showing my new design;

FIG. 2 is a front elevational view of the knife sharpener;

FIG. 3 is a right side elevational view of the knife sharpener;

FIG. 4 is a bottom plan view of the knife sharpener;

FIG. 5 is a rear elevational view of the knife sharpener; and,

FIG. 6 is a top, front and right side perspective view of the knife sharpener. 

The ornamental design for a knife sharpener, as shown. 